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Astronomers discover the closest black hole to Earth – in our cosmic backyard

Astronomers discover the closest black hole to Earth - in our cosmic backyard
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Artist's rendering of the closest black hole and its sun-like companion star

Astronomers have discovered the closest known black hole to Earth with the help of the International Gemini Observatory. It is also the first clear evidence of a dormant stellar-mass black hole in the Milky Way. Its proximity to Earth, just 1600 light-years away, offers an intriguing study target to advance our understanding of the evolution of binary systems. Image credit: International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva/Spaceengine/M. waste of time

The Gemini North telescope in Hawaii reveals the first stellar mass at rest[{” attribute=””>black hole in our cosmic backyard.

Using the International Gemini Observatory, astronomers have discovered the closest-known black hole to Earth. This is the first unambiguous detection of a dormant stellar-mass black hole in the Milky Way. Located a mere 1600 light-years away, its close proximity to Earth offers an intriguing target of study to advance our understanding of the evolution of binary systems.

“Take the Solar System, put a black hole where the Sun is, and the Sun where the Earth is, and you get this system.” — Kareem El-Badry

Black holes are the most extreme objects in the Universe. It is believed that supermassive versions of these unimaginably dense objects reside at the centers of all large galaxies. Stellar-mass black holes — which weigh approximately five to 100 times the mass of the Sun — are much more common. In fact, there are an estimated 100 million stellar-mass black holes in the Milky Way alone. However, only a handful have been confirmed to date, and nearly all of these are ‘active’. This means that they shine brightly in X-rays as they consume material from a nearby stellar companion, unlike dormant black holes which do not.

Astronomers have now discovered the closest black hole to Earth, which the researchers have dubbed Gaia BH1. To find it, they used the Gemini North telescope in Hawai‘i, one of the twin telescopes of the International Gemini Observatory, operated by NSF’s NOIRLab.

Gaia BH1 is a dormant black hole that is about 10 times more massive than the Sun and is located about 1600 light-years away in the constellation Ophiuchus. This means it is three times closer to Earth than the previous record holder, an X-ray binary in the constellation of Monoceros. The new discovery was made possible by making exquisite observations of the motion of the black hole’s companion, a Sun-like star that orbits the black hole at about the same distance as the Earth orbits the Sun.


This animation shows a Sun-like star orbiting Gaia BH1, the closest black hole to Earth, located about 1600 light-years away. Observations from Gemini North, one of the International Gemini Observatory’s twin telescopes operated by NSF’s NOIRLab, were crucial in constraining the orbital motion and therefore the masses of the two components in the binary system, allowing the team to identify the central body as a black hole about 10 times as massive as our sun. Source: T. Müller (MPIA), PanSTARRS DR1 (KC Chambers et al. 2016), ESA/Gaia/DPAC

“Take the solar system, put a black hole where the sun is and the sun where the earth is, and you get that system,” explained Kareem El-Badry, an astrophysicist at the Center for Astrophysics | Harvard & Smithsonian and the Max Planck Institute for Astronomy, and the lead author of the paper describing this discovery, published on 2 Monthly Bulletins of the Royal Astronomical Society.

“While there have been many claimed discoveries of systems like this, almost all of these discoveries have subsequently been disproved. This is the first clear detection of a Sun-like star in a wide orbit around a stellar-mass black hole in our galaxy.”

Although there are likely millions of stellar-mass black holes roaming the Milky Way, the few that have been spotted were discovered through their energetic interactions with a companion star. As material from a nearby star spirals toward the black hole, it becomes superheated, producing intense X-rays and jets of material. When a black hole isn’t actively feeding (ie, it’s dormant), it simply blends into its surroundings.

“I’ve been searching for dormant black holes for the past four years using a wide range of datasets and methods,” El-Badry said. “My previous attempts – as well as others – have uncovered a menagerie of binaries masquerading as black holes, but this is the first time the search has borne fruit.”

“While this potentially bodes for future discoveries of our galaxy’s predicted quiescent black hole population, the observations also leave a mystery to be solved — despite sharing a history with its exotic neighbor, why is the companion star so normal in this binary star system?” Martin Still

The team originally identified the system as potentially hosting a black hole by analyzing data from it The European Space Agency Gaia spaceship. Gaia captured the tiny irregularities in the star’s motion caused by the gravity of an invisible massive object. To study the system in more detail, El-Badry and his team turned to the Gemini Multi-Object Spectrograph instrument on Gemini North, which measured the companion star’s velocity as it orbited the black hole and provided an accurate measurement of its orbital period. Gemini’s follow-up observations were crucial in constraining the orbital motion, and therefore the masses, of the two components in the binary system, allowing the team to identify the central body as a black hole about 10 times the mass of our Sun.

“Our follow-up observations of Gemini unequivocally confirmed that the binary contains a normal star and at least one dormant black hole,” explained El-Badry. “We could not find any plausible astrophysical scenario that could explain the observed orbit of the system that does not involve at least one black hole.”

The team relied not only on Gemini North’s excellent observing capabilities, but also on Gemini’s ability to provide data on a tight schedule, given the team’s short window to conduct their follow-up observations.

“When we had the first indications that the system contained a black hole, we had only a week before the two objects were at their closest separation in their orbits. Measurements at this point are essential to make accurate mass estimates in a binary system,” El-Badry said. “Gemini’s ability to provide observations in a short amount of time was critical to the success of the project. If we had missed that narrow window, we would have had to wait another year.”

Astronomers’ current models of the evolution of binary systems do little to explain how the Gaia BH1 system’s peculiar configuration might have come about. In particular, the progenitor star that later turned into the newly discovered black hole would have been at least 20 times more massive than our sun. This means that it would have lived only a few million years. If both stars had formed at the same time, this massive star would have rapidly transformed into a supergiant, bloating and engulfing the other star before it had time to become a full-blown, hydrogen-burning main-sequence star like our Sun.

It’s not at all clear how the solar-mass star could have survived this episode and ended up as an apparently normal star, as observed by the black hole binary system observations. Theoretical models capable of surviving all predict that the solar-mass star should have landed in a much narrower orbit than is actually observed.

This may indicate that there are important gaps in our understanding of how binary black holes form and evolve, and also suggests the existence of an as yet unexplored population of quiescent binary black holes.

“It is interesting that this system cannot be easily adapted from standard binary evolution models,” concluded El-Badry. “It raises a lot of questions about how this binary system came about and how many of these dormant black holes are out there.”

“As part of a network of space- and ground-based observatories, Gemini North has not only provided strong evidence for the closest black hole yet, but also the first pristine black hole system unperturbed by the usual hot gas associated with the black hole,” said NSF Gemini Program Officer Martin Still. “While this potentially bodes well for future discoveries of our galaxy’s predicted quiescent black hole population, the observations also leave a mystery to be solved – despite sharing a history with its exotic neighbor, why is the companion star so normal in this binary star system?”

References: “A Sun-like star orbiting a black hole” by Kareem El-Badry, Hans-Walter Rix, Eliot Quataert, Andrew W. Howard, Howard Isaacson, Jim Fuller, Keith Hawkins, Katelyn Breivik, Kaze WK Wong, Antonio C .Rodriguez, Charlie Conroy, Sahar Shahaf, Tsevi Mazeh, Frédéric Arenou, Kevin B. Burdge, Dolev Bashi, Simchon Faigler, Daniel R. Weisz, Rhys Seeburger, Silvia Almada Monter and Jennifer Wojno, November 2, 2022, Monthly Bulletins of the Royal Astronomical Society.
DOI: 10.1093/mnras/stac3140

Gemini North observations were conducted under a director’s discretionary time program (Program ID: GN-2022B-DD-202).

The International Gemini Observatory is operated by a partnership of six countries including the United States through the National Science Foundation, Canada through the National Research Council of Canada, Chile through the Agencia Nacional de Investigación y Desarrollo, Brazil through the Ministério da Ciência, Tecnologia e Inovações, Argentina by the Ministerio de Ciencia, Tecnología e Innovación and Korea by the Korea Astronomy and Space Science Institute. These participants and the University of Hawaii, which has regular access to Gemini, each maintain a “National Gemini Office” to support their local users.

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